Reverse forming arrangement and method



Nov. 4, 1969 R. L. MARSHNER 3,475,944

REVERSE FORMING ARRANGEMENT AND METHOD Filed Dec. 30, 1966 v2Sheets-Sheet 1 ROBERT L. MARSHNER h INVENTOR ATTORNEY R. L. MARSHNERREVERSE FORMING ARRANGEMENT AND METHOD Nov. 4, 1969 2 Sheets-Sheet 2Filed Dec. 30, 1966 ROBERT L MARSHNER INVENTOR LL-D United States Patent3,475,944 REVERSE FORMING ARRANGEMENT AND METHOD Robert L. Marshner,9103 Simms Ave., Baltimore, Md. 21234 Filed Dec. 30, 1966, Ser. No.606,069 Int. Cl. B21d 22/20 US. Cl. 72-347 11 Claims ABSTRACT OFDISCLOSURE A method and apparatus for forming a folded cup from materialcapable of permanent plastic deformation to a self-holdingconfiguration, in which a mandrel having a thin flared head with anaxially non-straight smoothly arcuate rim surface is employed to applyan axial reverse drawing force on a central area of a tubular cup, thethin arcuate rim zone also applying a radial restraining force to thecup during the reverse drawing and enabling ease of withdrawal of themandrel from the cup after drawing.

This invention relates to an arrangement and method for reverse formingmetallic or other permanently plastically deformable cups, andparticularl cup seals which have a plurality of concentric tubular wallsin an intermediate or final configuration form.

In the formation of metallic cups by reverse drawing, a problem isencountered in the extraction of the forming mandrels from the re-shapedcup after partial or full reverse drawing. This results from the radialcompressive gripping action between the mandrel and the cup wall as themandrel draws the cup material thereabout. In smaller diameter cups ofone or two inches or the like or smaller in diameter this problem is notas aggravated as in larger diameter cups or cup seals, as for instancediameters of seven or eight inches or the like or larger. In the normalreverse drawing operation the mandrel is of the desired reverse drawndiameter for the cup along its effective length, even when the naturalroll radius is permitted to be formed by the material during the reversedrawing operation, :and the resulting compressive gripping forces by thecup on the straight walled mandrel are quite high, particularly in thelarger diameter cups, thereby posing a very substantial problem inremoval of the mandrel from the reverse drawn cup. It is accordingly amajor feature and advantage of this invention to provide an improvedmethod and arrangement for forming cups or cup seals, and particularlycup seals having multiple concentric tubular walls, in which the removalof the mandrel from the cup is materially facilitated through reductionof the gripping action on the mandrel, while enabling forming of thesame desired cup configuration.

Still other objects, features and attendant advantages will becomeapparent to those skilled in the art from a reading of the followingdetailed description, taken in conjunction with the accompanyingdrawings wherein:

FIGURE 1 is an exploded view in perspective of an embodiment of anarrangement according to the invention,

FIGURES 2-6 are schematic illustrations of the practice of the methodaccording to the invention,

FIGURE 7 is an illustration of a modified application of the methodaccording to the invention.

Referring now in detail to the figures of the drawings, as shown in theexploded view of FIGURE 1 a flared headed mandrel 11 is employed toreverse draw a cup 21 which is adapted to be slidably removably disposedwithin a guide block 41 having a guide cap 51 removably fittingthereover for guiding of the flared headed mandrel 11 during the reversedrawing operations.

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The flared headed mandrel 11 has a flat head 13, and a reduced diametersmooth surfaced neck 15 on which is formed a threaded neck section 15afor receiving an adjustable stop nut 31, which adjustment may have aninterference fit for secure adjustment. The smaller diameter end 15b ofthe mandrel 11 is preferably flat for advantageous application of forcethereto in the forming operation on cup 21. The flared head 13 of themandrel has a smoothly rounded annular rim 13a, and has a flat endsurface 13b corresponding to the flat surface size desired in the end ofthe tubular portion of the cup upon completion of the reverse formingoperation. In addition, the radius of curvature of the smoothly roundedannular rim 13a corresponds to the desired radius of curvature of thereverse formed cup at the zone of annular interconnection between thereverse formed cup end wall 21b (see FIG- URE 3) and the integrallyadjoining inner tubular wall section 21a. This longitudinally roundedrelatively thin rim configuration also aids in ease of removal,particularly when rocking removal motion is required, as laterdescribed. While other relative diameters may be employed and stillyield some of the benefits of the invention, it is most advantageous anddesirable that the outer diameter of the head 13 from rim-to-rim indiameter of the head 13 correspond to the diameter which will enable thecup to form a natural roll radius along the reversal zone 21] betweenthe outer and inner cup sections 21a, 21a. This diameter for the mandrelhead 13 can be determined for practical purposes by application of thefollowing empirical formula:

where D is the original diameter of the cup 21 before the particularreverse drawing operation to be effected by the mandrel 11, t is thethickness of the tubular wall section 21a to be formed by the reversedrawing of the cup 21 by the mandrel 11, and consequently is also thediameter of the flared mandrel head 13.

Guide block 41 has a cylindrical bore 43 which terminates in a shoulder49 at one end thereof formed by an end wall 45 having a central opening47. The guide cap 51 has an annuar skirt 53 which is slidably removablycomplementary to the guide block 41. A central guide bore 55 is formedin the end wall of the guide cap 51 for guiding the reduced diameterneck 15 of the mandrel 11 in the reverse forming of the cup. In theoperation of the method of the invention employing this apparatus, thecup 21 is slidably inserted into the cylindrical bore 43 in guide block41, the cup preferably having an outer diameter D which is generallycomplementary to and provides an easy slip fit with the annular sidewall of the cylindrical bore 43. The cup is seated with its open end 21cfacing the central opening 47 in the guide block 41, and the seated edgesurface abuts against the shoulder 49. Guide cap 51 is thereupon placedover the upper end of the guide block 41, with the flared headed mandrel11 having its reduced diameter neck 15 slidably disposed in the guidebore 55, and its flared head 13 resting on the closed end wall 21b ofthe cup 21, as shown in FIGURE 2 The adjustable stop nut 31 may beadjusted to the desired position along the length of the threadedsection 15a of the mandrel neck to provide the desired termination ofmotion of the mandrel and length for the inner cup tubular wall section21a, or alternatively the flat supporting surface on which the guideblock 41 is supported may in some instances serve as a stop fortermination of the reverse drawing stroke motion of the cup 21, and/orfor seating of the open end cup edge surface thereon.

In carrying out the method according to the invention, an axial force Fis applied to the mandrel 15 as indicated 3 in FIGURES 3 and 4, and thecup 21.is thereby caused to plastically deform and roll through anannular reverse bend 21] to a reduced diameter inner tubularconfiguration 21a, the reduced diameter end wall 21b corresponding tothe shape and size of the end of the flared head 13 of the mandrel.Force F is continued to be applied until the mandrel reaches the desiredstop position, which in the case of cup seals may be at any desiredintermediate position which provides a desired length for each of theouter wall 21a and inner wall 21a, such as that configurationillustrated in FIGURES 46. Upon completion of the forming motion of themandrel the force F is removed and the guide cap 51 is removed from theguide block 41. This may normally be effected by exerting a relativelysmall pulling force on each of the guide cap and guide block, althoughin some instances it may also be desirable to exert a separating forceon the reduced diameter end wall 21b in a direction toward the end cap51 by application of a force through the central opening 47 of the guideblock 41. In this separating operation the formed cup 21 is normallycarried with the mandrel 11 and cap 51, as illustrated in FIGURE 5, andit thereupon remains only to exert a relatively small axial pullingforce on the cup 21 in removing it from the flared head 13, or to rockthe cup 21 away from the head 13 as shown in FIGURE 6. This is facilelyaccomplished in either case, as the compressive retaining forces arevery materially reduced in the case of the head 13 as compared to theconventional straight mandrel, and also the rocking action isfacilitated as will be noted by the reduced neck portion 15, whereassuch cannot be effected with the normal straight sided mandrel. Forinstance, it has been found that an 8-inch mandrel of conventionalstraight walled construction requires 2 to 3 tons of removal force,whereas the extraction force with the present arrangement and method isreduced to approximately 100 pounds, and in many instances the removalof the mandrel from the completed cup form can be accomplished by hand.It will be appreciated, however, that these reduced extraction forcesare only reduced to this minimum when the reversal diameter correspondsto that diameter d indicated in the equation previously discussed,whereby the reverse drawing is allowed to proceed through a naturalreverse bend roll radius. Any substantial reduction of this natural rollradius formation will of course result in a tighter fit of the mandrelhead within the reduced diameter tubular section, with consequentincreased extraction force being required, although still beingsubstantially less than that which would be required for a straightsurfaced forming mandrel. Not only is the extraction force materiallyreduced by employing this invention, but also the time required toextract the mandrel is substantially reduced, and one can employ reducedcapacity equipment in effecting the process, particularly the extractionaspect.

In FIGURE 7 is shown a modified application of the method, in which theadjustable stop nut 31 is adjusted to a position on the mandrel neck 15such that the end of the reverse forming stroke occurs at anintermediate position between the ends of the final outer tubular wallsection 21a, thereby providing a cup seal which when employed in anarrangement such as shown in US. Patents 3,106,131 and 3,119,302 willhave a reduced expansion stroke as compared to the expansion stroke ofthe final cup 21 resulting from the application of the method asillustrated in FIGURE 4 in which the inner tubular section 21a isrelatively longer than the final outer tubular section 21a.

It will be apparent that greater or lesser length or difference inlength between the outer and inner tubular sections of the cup may beobtained as desired, and further additional smaller headed mandrels maybe employed for further reverse forming the cup to a further interfoldedreverse drawn position by application of the smaller diameter headedmandrel in the opposite direction against the resulting reduced diameterend wall 21b, in which case the annular bend 21 may rest against theshoulder 49 of the guide block 41, the shoulder 41 being madesufficiently wide to accommodate this engagement as may be necessary, orsuch may rest against the supporting surface 61, or a suitable smoothwalled annular groove in the supporting surface 61 or a modifiedshoulder 49 to accommodate the annular bend 21) during this additionalreverse forming operation.

While the invention has been described with respect to a singleembodiment and several modes of practice of the invention, it will beapparent to those skilled in the art that various modifications andimprovements may be made without departing from the scope or spirit ofthe invention. Accordingly, it is to be appreciated that the inventionis not to be limited by the illustrative embodiment and mode ofpractice, but only by the scope of the appended claims.

That which is claimed is:

1. The method of forming a cup from material capable of permanentplastic deformation to a self-holding configuration, comprising:

applying, through the medium of an annular force-applying head ofsmaller axial thickness at the rim zone than in rim diameter and with anaxially non-straight smoothly axially convexly arcuate rim surface, anaxial reverse drawing force on a central area of the closed end of atubular cup having one closed end and an opposite open end,

reverse drawing said cup to a depth greater than the axial rim zonethickness of said force-applying head by application of said force to areverse drawn length substantially greater than the cup-engagingthickness of said force-applying head while applying a radialrestraining force to said cup by said smoothly axially arcuate rim zonesurface on said head,

and separating said head from said cup.

2. The method according to claim 1, said separation being effected byapplying opposing axial separating forces on said cup and said head.

3. The method according to claim 1, said separation being effected byapplying opposing axial separating forces on said cup and said headwhile rocking said cup to disengage it from said head.

4. The method according to claim 1, said reverse-drawing force beingapplied while containing the longitudinal walls of said cup within acircumscribing radial-movement-restraining surface.

5. The method according to claim 1, including terminating said reversedrawing of said cup prior to drawing of the original cup form fully intothe smaller diameter reverse drawn form, to thereby form a reverse-drawncup having an outer tubular section and an inner tubular sectionintegrally interconnected by a smooth annular reverse bend, the innertubular section being closed at one end,

and applying a further reverse drawing force to said inner tubularsection in the opposite direction, through the medium of a forceapplying head as in claim 1 in which the circular area of application ofthe force is smaller than the closed end of said inner tubular section,

terminating application of said further reverse drawing force prior toreverse-drawing of said inner tubular section fully into the nextsmaller opposite reverse drawn form to thereby form a reverse drawn cuphaving three concentric tubular sections sequentially integrallyinterconnected at their opposite ends,

and removing said cup from said head by application of axial separationforces to said head and said cup.

6. The method according to claim 1, said application of reverse drawingforce to said cup by said head being effected by application of force toa central area on said head of substantially smaller area than theeffective reverse draw force-applying of said head to said cup, the

circumferential spatial zone surrounding and between said smallercentral area of force application on said head and the larger area ofhead applied force being open in the zone behind said head to therebyreduce the radial gripping engagement of said cup with said head in thecourse of reverse drawing and to minimize the required separation forcebetween cup and head, as well as enabling rocking of said cup on saidhead during removal as may be required.

7. The method according to claim 1, said reverse drawing force beingapplied to a central area on said closed cup end of smaller diameter dthan the outer diameter D of said cup by an amount permitting formationof the natural roll radius of the cup material during said reversedrawing of the material from the original cup wall form to the inner cupwall form.

8. The method according to claim 7, said smaller diameter d beingsubstantially where t is the thickness of said cup wall.

9. A reverse drawing arrangement for reverse drawing cups comprising:

a guide block having a cylindrical bore for receiving a cup,

a force-applying reverse-draw mandrel having a flared head at one endfor applying reverse-drawing force to a cup when disposed in said bore,

said mandrel head being of smaller diameter than said cylindrical boreby an amount suflicient to enable the formation of a natural roll radiusin reverse drawing a given cup within said bore,

said mandrel having a reduced diameter neck formed behind said flaredhead of substantially longer length than said head length,

said flared head having a rounded rim zone of smooth non-straightaxially arcuate curvature and being of substantially less axial lengthat its rim zone than in rim diameter.

10. A reverse drawing arrangement for reverse drawing cups comprising:

a guide block having a cylindrical bore for receiving a a force-applyingreverse-draw mandrel having a flared head at one end for applyingreverse-drawing force to a cup when disposed in said bore,

said mandrel head being of smaller diameter than said cylindrical boreby an amount suflicient to enable the formation of a natural roll radiusin reverse drawing a given cup within said bore,

said mandrel having a reduced diameter neck formed behind said flaredhead of substantially longer length than said head length,

said fiared head having a rounded rim zone and being of substantiallyless axial length at its rim zone than in rim diameter,

said mandrel having a threadedly adjustable stop formed thereon rearwardof said flared head,

said guide block having a radially inwardly extending annular shoulderat one end of said bore and forming a longitudinal central opening insaid guide block,

and a guide cap removably disposed on the opposite end of said guideblock,

said guide cap having a central guide bore therein coaxial with saidguide block bore and of complementary sliding fit with said mandrel neckfor guid ing of said mandrel during application of force thereby to acup which may be in said guide block bore.

11. An arrangement according to claim 9,

the relationship of the mandrel head diameter d rela tive to theeflective cup diameter D being substantially where t is the thickness ofthe cup wall to be drawn.

References Cited UNITED STATES PATENTS 830,193 9/1906 Anderson 723481,187,461 6/1916 Knox 72348 1,649,841 11/1927 May 72 34s 2,179,19411/1939 Passmore 72-347 3,139,670 7/1964 George 72348 RICHARD J. HERBST,Primary Examiner

